EGNOS Open Service

EGNOS
Title	EGNOS Open Service
Author(s)	GMV.
Level	Basic
Year of Publication	2011

The EGNOS Open Service consists of a set of signals for timing and positioning intended for general purpose applications. It is fully accessible by means of a GPS/SBAS compatible receiver, it is free of charge and it does not require any receiver specific certification nor authorization.

Introduction

The EGNOS Open Service was declared available in October 2009

The EGNOS Open Service consists of a set of signals for timing and positioning intended for general purpose applications. It is fully accessible by means of a GPS/SBAS compatible receiver, it is free of charge and it does not require any receiver specific certification nor authorization. Details about the EGNOS-enabled receiver design specifications can be found in EGNOS Receiver specficatoin document.

This service is provided through the GEO satellites within the EGNOS service area and it improves GPS performances in Europe. However, EGNOS OS shall only be used for non safety critical purposes, i.e. those where degraded performances could not provoke personal damage. Besides, no service guarantee or liability is provided by the EGNOS Service provider, the European Commission or the European Space Agency (ESA).

Lance Armstrong´s arrival at the Summit of Alpe d´Huez where riders were tracked with EGNOS

The EGNOS Open Service is the first EGNOS service to become available and its main objective is to obtain enhanced positioning accuracy by correcting the error contributions that affect GPS signals, which are related to satellite clocks, satellite payload induced signal distortion, satellite position uncertainties and ionospheric delays whereas other effects, such as tropospheric delays, multipath or user receiver contributions, are local effects and cannot be corrected by an SBAS system.

EGNOS OS is accessible in Europe to any user equipped with an appropriate GPS/SBAS compatible receiver for which no specific receiver certification is required.

The OS was declared available on the 1st October 2009 and this EGNOS service is intended to be provided for a minimum period of 20 years with a 6 years in advance notice in case of significant changes in the Services provided.

Performance requirements

EGNOS Performances are considered from a user perspective and they are expressed in terms of availability, continuity, integrity and accuracy. The minimum requirements for these terms are defined by SBAS standards which were conceived for civil aviation applications. These standards are called SBAS Minimum Operational Performance Standards and are published by RTCA under the reference DO-229.

Consequently, MOPS intends to support aviation use and provides a series of features to guarantee integrity which, as expressed in EGNOS Service Definition Document, may result in degraded performance over what could be reached if implementing a tailored processing of EGNOS signals for OS, due to the stringent aviation requirements.

In any case, all SBAS receivers expected to support OS shall as define in :

• Use the Geostationary satellite ranging function if available (broadcast through message types 9 and 17, this function is currently not supported by EGNOS).
• Decode and apply satellite clock corrections (broadcast through message types 2-5 and corresponding to satellites selected by message type 1).
• Decode and apply satellite ephemeris corrections (broadcast through message types 24- 25).
• Decode and apply ionospheric corrections (broadcast through message type 26 for ionospheric grid points selected by message type 18).
• Take into account major warnings sent through the SBAS messages (broadcast through message types 2-5 and 6).

Additionally, an OS receiver may use the content of message type 12, if used for time determination.

In order to define OS user performances, a number of assumptions are made:

• The user receiver shall implement MOPS DO-229 navigation weighted solution.
• The EGNOS receiver shall take into account the monitoring of satellites and Ionospheric Grid Points according to the UDRE/GIVE indicators processed.
• A clear sky environment is assumed with no obstacles masking satellite visibility greater than 5° above the local horizontal plane.

The minimum level of performance against which the system has been designed, as well as data of actual performance, is provided in the table and map bellow. As stated in these data is solely presented for transparency in order to enable the user to make an informed decision regarding EGNOS OS use and, thus, actual EGNOS OS performance may differ in the future.

	Definition	Value
Horizontal Accuracy	Corresponds to a 95% confidence bound of the bi-dimensional position error in the horizontal local plane for the worst user location.	3 m
Vertical Accuracy	Corresponds to a 95% confidence bound of the uni-dimensional unsigned position error in the local vertical axis for the worst user location.	4 m